Method and system for pumping liquid from an offshore natural gas production well

ABSTRACT

A pump assembly comprises a first piston near a lower end of a coiled water and/or other condensed liquid discharge conduit, which is actuated by second and third pistons that are arrange at the upper and lower ends of a hydraulic or pneumatic fluid conduit, wherein the third piston is connected to a floating body, which is oscillated by waves, such that a pair of one way check valves suck and push production water and other condensed liquids sequentially from a lower region of the well into a lower portion and subsequently into an upper portion of the coiled water and other condensed liquid outlet conduit.

BACKGROUND OF THE INVENTION

The invention relates to a method and system for pumping liquid from an offshore natural gas production well.

Natural gas generally comprises methane, ethane, condensates (C4-C6), water and other condensable components, which may condensate in the well, where the ambient pressure and temperature is lower than in the pores of the natural gas containing formation. The condensed water and other liquids may drip down back to and accumulate in the inflow region of the well, thereby gradually drowning and killing gas production from the well.

It is known to remove condensed water and other liquids from a gas well using an Electrical Submersible Pump (ESP), which may be connected to a coiled water discharge conduit which is suspended in the interior of the inflow region of the well.

A problem with the known water removal ESP pump is that an offshore natural gas production facility may not have electrical power facilities for generating electrical power for the ESP, that electrical ESPs and the electrical power supply cables may cause sparking and are therefore dangerous for use in gas wells.

It is furthermore known from U.S. Pat. No. 7,198,099 to inject a foaming agent into the inflow region of the well, which induces produced water and other liquids to form a foam, which has a low density and is easily lifted to surface.

A problem with the known foam lifting method is that the produced foam is contaminated with hydrocarbons, such as hydrates, condensates and paraffins, which cannot be disposed into a sea or other body of water and therefore need to be collected in large foam collection tanks, which need to be inspected and emptied regularly, which is a complex and time consuming activity, in particular on unmanned offshore satellite gas production platforms at remote locations.

It is an object of the present invention to solve these problems and to provide an improved and safe method and system for removing water and other condensed liquids from an offshore natural gas production well, which can be deployed without requiring electrical power supply lines, without carbon dioxide emissions and without requiring large foam collection tanks.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a method for pumping liquid from an offshore natural gas production well by means of a pump assembly that is actuated by wave energy derived from waves in a body of water surrounding an upper section of the well.

Optionally, the pump assembly comprises a positive displacement pump, which is actuated to reciprocate in response to waves in the body of water, such as an ocean, sea, lake or river, surrounding an offshore gas production facility, such as a platform, to which the upper section of the well is connected.

The pump assembly comprises a positive displacement pump, which is arranged near a bottom of the well and is connected to a hydraulic or pneumatic power transfer conduit, which is connected to a positive displacement motor assembly that is arranged in the body of water.

The pump and motor assemblies each comprise piston and cylinder assemblies, which are interconnected by the hydraulic or pneumatic power transfer conduit.

The piston of the piston and cylinder assembly of the motor assembly may be arranged in a wave zone near the upper surface of the body of water, such that the piston is induced to oscillate in the cylinder in response to oscillating movement of the body of water at or near the upper surface thereof.

A natural gas with a reduced production and/or other liquid content may be produced through the production tubing surrounding the coiled tubings without requiring electrical power supply lines and foam injection facilities.

In accordance with the invention there is furthermore provided a system for inhibiting liquid loading in an offshore natural gas production well by pumping liquid from the well, the system comprising a pump assembly that is actuated by wave energy.

The pump assembly may comprise a reciprocating pump, which is configured to reciprocate in response to waves in a body of water, such as an ocean, sea, lake or river, surrounding an offshore gas production facility, such as a platform, to which the well is connected.

The reciprocating pump may comprise a positive displacement pump arranged near a bottom of the well and is connected to a hydraulic or pneumatic power transfer conduit, which is connected to a positive displacement motor that is arranged in the body of water.

The pump and motor assemblies may each comprise piston and cylinder assemblies, which are connected to each other by the hydraulic or pneumatic power transfer conduit.

The piston of the piston and cylinder assembly of the motor may be connected to a floating body arranged in a wave zone near the upper surface of the body of water, such that the piston of the motor is induced to oscillate in the cylinder of the motor in response to waves at the upper surface of the body of water induced by wind, current and/or tides.

It is preferred that the pump comprises a first piston near a lower end of a coiled water and/or other condensed liquid discharge conduit, which is actuated by second and third pistons of the motor that are arrange at the upper and lower ends of a hydraulic or pneumatic power transfer conduit, wherein the third piston is connected to a floating body, which is oscillated by waves, such that a pair of one way check valves suck and push production water and other condensed liquids sequentially from a lower region of the well into a lower portion and subsequently into an upper portion of the coiled water and other condensed liquid outlet conduit.

These and other features, embodiments and advantages of the method and/or system according to the invention are described in the accompanying claims, abstract and the following detailed description of a preferred embodiment disclosed in the accompanying drawing in which reference numerals are used which refer to corresponding reference numerals that are shown in the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic longitudinal sectional view of an offshore gas production well and facility wherein the method and system according to the invention are used.

DETAILED DESCRIPTION OF THE DEPICTED EMBODIMENT

FIG. 1 shows an offshore gas production well 1 which comprises upper and lower well casings 2A, 2B and a wellhead 3 from which a production tubing 4 is suspended. The well comprises an upper section 1A, which is surrounded by a body of water 11, such as an ocean, sea, lake, or river, and a lower section 1B, which penetrates the water bottom 12 and extends into a wet natural gas containing earth formation 5.

A stream of wet natural gas (CH₄+H₂O) is produced from the wet gas containing earth formation 5, which stream flows from an inflow region 6 near the bottom of the well 1 into the production tubing 4. The stream of wet gas expands and thereby cools within the inflow region 6 and production tubing 4, which causes condensation of water (H₂O) and other condensable components, such as hydrates, condensates (C₂-C₆), and/or other hydrocarbons, such as aphaltenes, which drip down to the bottom of the well and may form an aqueous liquid pool 8 at the bottom of the inflow region 6 of the well 1.

The condensed water and other liquid components are pumped from the aqueous liquid pool 8 to surface through a coiled water discharge conduit 10.

The coiled water discharge conduit 10 has a closed lower end 10A in which a one-way check valve 13 is arranged, which check valve 13 permits condensed water and/or other liquids to flow from the pool 8 into the interior of the coiled tubing 10, but which blocks reverse flow of water and/or other liquids from the interior of the coiled tubing 10 into the pool 8.

A first piston 14 comprising a second one way check valve 15 is arranged between a lower section 10 B and an upper section 10C of the interior of the coiled water discharge conduit 10. The second one way check valve 15 permits water and/or other liquids to flow up from the lower section 10B into the upper section 10C of the production tubing 10 when the first piston 14 is induced to move down through the interior of the coiled water discharge conduit 10, whereas the second one way check valve 15 blocks reverse flow of water and/or other liquids from the upper section 10C into the lower section 10B of the production tubing 10.

The first piston 14 is actuated to oscillate up and down within the interior of the coiled water discharge conduit 10 by a downhole piston and cylinder assembly 16A, 16B, wherein the interior of the cylinder 16C below the second piston 16A is connected via a port opening 17 passing through the walls of the cylinder 16B and the coiled water discharge conduit 10 to the interior of an outer coiled tubing 20, which is coaxially arranged around the coiled water discharge conduit 10. The outer coiled tubing 20 is at its upper end connected to a hydraulic or pneumatic power transfer conduit 21, which has a substantially vertical lower end 21A in which a third piston 22 is arranged. The third piston 22 is connected to a piston rod 23, which is connected by a set of spacer bars 24 to an annular shaped floating body 25, which is filled with low-density foam that has a lower density than the surrounding body of water 11.

The floating body 25 is arranged at the upper surface of the body of water 11, so that waves 33 due to wind, current and/or tides will induce the floating body 25, and the third piston 22, which is connected thereto, to oscillate up and down, as illustrated by arrow 30.

The oscillating movement of the third piston 22 will induce the pneumatic or hydraulic fluid 32, such as water, air, nitrogen or another liquid, gas or fluid mixture in the interior of the power transfer conduit 21 and the outer coiled tubing 20 to oscillate up and down as illustrated by the arrows 28.

Thus, each upward movement of the floating body 25 due to a rising wave 33 will push the third piston 22 up and thereby cause the hydraulic or pneumatic fluid 32 to push the first and second pistons 14, 16A up. The upward motion of the first piston 14 will induce the second one way check valve 15 to close and water and other condensed liquids to be sucked into the lower portion 10B of the coiled water discharge conduit 10 through the first one way check valve 13.

Subsequently, each downward movement of the floating body 25 due to a falling wave 33 will push the third piston 22 down and thereby cause the hydraulic or pneumatic fluid 32 to suck the first and second pistons 14, 16A down. The downward motion of the first piston 14 will induce the second one way check valve 15 to open and the first one way check valve 14 to close such that water and other condensed liquids are discharged through the second one way check valve 15 from the lower portion 10B of the coiled water discharge conduit 10 into the upper portion 10C of the coiled water discharge conduit 10.

It will be understood that the method and system according to the invention provide a water and other liquid discharge system, which does not require electrical power supply, does not generate carbon dioxide emission and does not require large foam collection tanks. 

1. A method for pumping liquid from an offshore natural gas production well by means of a pump assembly that is actuated by wave energy derived from waves in a body of water surrounding an upper section of the well.
 2. The method of claim 1, wherein the pump assembly comprises a positive displacement pump, which is actuated to reciprocate in response to waves in the body of water, such as an ocean, sea, lake or river, surrounding an offshore gas production facility, such as a platform, to which the upper section of the well is connected.
 3. The method of claim 2, wherein the pump assembly comprises a positive displacement pump, which is arranged near a bottom of the well and is connected to a hydraulic or pneumatic power transfer conduit, which is connected to a positive displacement motor assembly that is arranged in the body of water.
 4. The method of claim 3, wherein the pump and motor assemblies each comprise piston and cylinder assemblies which are interconnected by the hydraulic or pneumatic power transfer conduit.
 5. The method of claim 4, wherein the piston of the piston and cylinder assembly of the motor assembly is arranged in a wave zone near the upper surface of the body of water, such that the piston is induced to oscillate in the cylinder in response to oscillating movement of the body of water at or near the upper surface thereof.
 6. The method of claim 3, wherein the pump assembly is connected to a first and second coiled tubing, which are suspended from a wellhead through the interior of a production tubing in the well, the first coiled tubing forms part of the hydraulic or pneumatic power transfer conduit between the positive displacement pump and motor assembly, and the second coiled tubing provides a production water and/or other liquid outlet conduit for discharging production water and/or other liquid from the bottom of the gas well to a production water and/or other liquid disposal facility.
 7. The method of claim 6, wherein a natural gas with a reduced production and/or other liquid content is produced through the production tubing surrounding the coiled tubings.
 8. The method of claim 6, wherein the coiled tubings are substantially coaxial relative to each other.
 9. The method of claim 8, wherein the second coiled tubing is arranged in the interior of the first coiled tubing.
 10. A system for inhibiting liquid loading in an offshore natural gas production well by pumping liquid from the well, the system comprising a pump assembly that is actuated by wave energy.
 11. The system of claim 10, wherein the pump assembly comprises a reciprocating pump, which is configured to reciprocate in response to waves in a body of water, such as an ocean, sea, lake or river, surrounding an offshore gas production facility, such as a platform, to which the well is connected.
 12. The system of claim 11, wherein the reciprocating pump comprises a positive displacement pump arranged near a bottom of the well and is connected to a hydraulic or pneumatic power transfer conduit, which is connected to a positive displacement motor that is arranged in the body of water.
 13. The system of claim 12, wherein the pump and motor assemblies each comprise piston and cylinder assemblies which are connected to each other by the hydraulic or pneumatic power transfer conduit.
 14. The system of claim 13, wherein the piston of the piston and cylinder assembly of the motor is connected to a floating body arranged in a wave zone near the upper surface of the body of water, such that the piston of the motor is induced to oscillate in the cylinder of the motor in response to waves at the upper surface of the body of water induced by wind, current and/or tides.
 15. The system of claim 14, wherein the pump comprises a first piston near a lower end of a coiled water and/or other condensed liquid discharge conduit, which is actuated by second and third pistons of the motor that are arrange at the upper and lower ends of a hydraulic or pneumatic power transfer conduit, wherein the third piston is connected to a floating body, which is oscillated by waves, such that a pair of one way check valves suck and push production water and other condensed liquids sequentially from a lower region of the well into a lower portion and subsequently into an upper portion of the coiled water and other condensed liquid outlet conduit. 